package Problem;

import java.util.Scanner;

//
// Created by ✎﹏ℳ๓独赏☆独醉 on 2024/1/26.
// 
public class 金币 {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int num = scan.nextInt();
        long sum = 0;
        int day = 1;
        flag:for (int i = 1; ; i++) {
            for (int j = 1; j <= i; j++) {
                sum+=i;
                day++;
                if(day > num){
                    break flag;
                }
            }
        }
        System.out.println(sum);
    }

}
